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Commit 9f986a8c authored by David Brownell's avatar David Brownell Committed by Linus Torvalds
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Documentation/ABI: /sys/class/gpio 



Provide summary ABI docs about the /sys/class/gpio files.

Signed-off-by: default avatarDavid Brownell <dbrownell@users.sourceforge.net>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5bead2a0

Documentation/ABI/testing/sysfs-gpio

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What:		/sys/class/gpio/

Date:		July 2008

KernelVersion:	2.6.27

Contact:	David Brownell <dbrownell@users.sourceforge.net>

Description:



  As a Kconfig option, individual GPIO signals may be accessed from

  userspace.  GPIOs are only made available to userspace by an explicit

  "export" operation.  If a given GPIO is not claimed for use by

  kernel code, it may be exported by userspace (and unexported later).

  Kernel code may export it for complete or partial access.



  GPIOs are identified as they are inside the kernel, using integers in

  the range 0..INT_MAX.  See Documentation/gpio.txt for more information.



    /sys/class/gpio

	/export ... asks the kernel to export a GPIO to userspace

	/unexport ... to return a GPIO to the kernel

	/gpioN ... for each exported GPIO #N

	    /value ... always readable, writes fail for input GPIOs

	    /direction ... r/w as: in, out (default low); write: high, low

	/gpiochipN ... for each gpiochip; #N is its first GPIO

	    /base ... (r/o) same as N

	    /label ... (r/o) descriptive, not necessarily unique

	    /ngpio ... (r/o) number of GPIOs; numbered N to N + (ngpio - 1)